The present invention generally relates to methods and systems for providing cardiac pacing therapy. More particularly, the invention concerns methods and implantable stimulation devices to detect onset of orthostatic hypotension.
When an individual changes from a horizontal or supine position to a sitting or standing position, the cardiovascular system must make frequent and rapid adjustments to blood pressure and heart rate. When such adjustments are not accomplished, orthostatic hypotension occurs. Orthostasis means upright posture, and hypotension means low blood pressure. Thus, orthostatic hypotension describes the effects caused by low blood pressure when changing from a lying to upright position. Orthostatic hypotension is defined as a decrease of at least 20 mm Hg in systolic blood pressure when an individual moves from the horizontal to upright position.
The symptoms of orthostatic hypotension include dizziness, faintness, or lightheadedness that appear when standing. Other symptoms that often accompany orthostatic hypotension include chest pain, trouble holding urine, impotence, and dry skin from loss of sweating. Some patients with severe orthostatic hypotension are severely incapacitated.
Ideally, a cardiac stimulation device would detect conditions that might give rise to orthostatic hypotension and rapidly transition to an increased pacing rate to counteract the effects of orthostatic hypotension. Unfortunately, detecting the onset of orthostatic hypotension is not an easy task. Moving from a horizontal position to an upright position takes place in a very short time frame. For effective treatment, the cardiac stimulation device should be able to detect the conditions accurately and administer the pacing therapy in a very short period of time.
Accordingly, there is a need for improved detection techniques for accurately detecting the onset of orthostatic hypotension to allow for timely administration of pacing therapy.
An implantable cardiac stimulation device is programmed to administer pacing therapy in response to a postural change in a patient""s position and a confirmation of that postural change using a cross-check parameter. The pacing therapy is an increase in the cardiac pacing rate to counteract effects of orthostatic hypotension.
In the described implementation, the cardiac stimulation device is equipped with a position sensor to sense a position parameter indicative of when a patient changes from a horizontal position to an upright position, such as when moving from a sleeping or reclined posture to a sitting or standing posture. One example of a position sensor is a 3D accelerometer that detects bodily orientation in three dimensions.
The cardiac stimulation device is further equipped with additional sensors and a data acquisition system to monitor at least one cross-check parameter that is affected or modulated by changes in the patient""s position. The cross-check parameter is used to confirm that a postural change of the sort that might induce orthostatic hypotension did occur. In one implementation, the cross-check parameter is an evoked response parameter (ERP) functionally related to the evoked response amplitude (ERA) measured in the right ventricle. The device computes a delta ERP (xcex94ERA) as a function of the ERP and the moving average of the ERP. By examining changes in the xcex94ERP during approximately the time when the postural change is detected by the position sensor, the device can confirm or deny occurrence of a significant postural change.
The cardiac stimulation device includes a processor operably coupled to the position sensor, other sensors, and data acquisition system. The processor is programmed to determine when to administer cardiac pacing therapy to the patient based on the position parameter and the cross-check parameter. For instance, the processor applies an increased pacing rate effective to treat orthostatic hypotension when the device (1) detects a postural change from a horizontal position to an upright position and (2) confirms that postural change via the cross-check parameter, such as changes in the ERP.